The present disclosure relates to a light deflector used in forming an electrostatic latent image and the like, a light deflector manufacturing method and an optical scanning device with such a light deflector.
In an electrophotographic image forming apparatus, a light beam modulated in accordance with image data is generated, reflected and deflected, whereby an image bearing member such as a photoconductive drum is scanned with the deflected light beam to form an electrostatic latent image. The light deflector is a device for reflecting and deflecting a light beam. A technique using MEMS (Micro Electro Mechanical Systems) mirrors as a light deflector instead of a polygon mirror has been proposed. The MEMS mirrors have an advantage of speeded-up scanning, low power consumption and the like.
The light deflector using the MEMS mirrors includes a torsion bar, mirror portions swingable about an axis of the torsion bar and mirror drivers.
Upon the input of drive signals to the mirror drivers, the mirror drivers resonate (vibrate) movable portions of the MEMS mirrors to swing the mirror portions about the axis of the torsion bar and, in this state, a light beam incident on the mirror portions is reflected and deflected to scan the light beam. The movable portion of the MEMS mirror is, in other words, a vibration system of the MEMS mirror and configured by the mirror portion and the torsion bar.
In the case of using the MEMS mirrors by setting the frequencies of the drive signals to be input to the MEMS mirrors at the same value for each MEMS mirror, a resonant frequency of the movable portion of the MEMS mirror (hereinafter, merely referred to as a resonance frequency in some cases) needs to be adjusted for each MEMS mirror. This is because a maximum deflection angle of the mirror portion differs for each MEMS mirror if the resonant frequency differs.
The resonant frequency is determined by a moment of inertia of the mirror portion, a spring constant of the torsion bar and the like. The resonant frequency changes if these physical quantities only slightly differ. For example, dimensions of the mirror portion affect the moment of inertia of the mirror portion, and the resonant frequency changes if the dimensions of the mirror portion differ from design values by several microns. Since errors in the above physical quantities unavoidably occur in the manufacturing of the MEMS mirror, the resonant frequency needs to be adjusted.
There have been proposed a technique for adjusting a resonant frequency by reducing a mass of a movable portion of a MEMS mirror and a technique for adjusting a resonant frequency by increasing a mass of a movable portion of the MEMS mirror.
The former technique adjusts the resonant frequency by providing a first area and a second area, which are symmetrical with respect to a torsion bar, forming a plurality of mass bodies in advance in the respective areas, selectively cutting off the mass body by a laser beam to reduce the mass of the movable portion of the MEMS mirror.
The latter technique adjusts the resonant frequency by making the mirror portion larger toward both left and right sides, providing a first area and a second area symmetrical with respect to a torsion bar, depositing and curing a liquid in each area to selectively form a mass body and increase the mass of the movable portion of the MEMS mirror.